In a statement, Leon insisted the UAE, Qatar, Turkey, and Egypt "have consistently supported UN peace efforts" in Libya, and stressed the need to be "extremely cautious" about reports of a UAE violation of the arms embargo.

"I have decided to request a full clarification of the issue, including from the United Arab Emirates authorities, as I take time to reflect on the next steps in my professional career," said Leon in a statement released on Friday.

"Given the inaccurate or false information we have seen in previous months regarding the process in Libya and the UN and my role, I believe it is imperative to be extremely cautious about the most recent reports... The authorities and government of the UAE have the right and deserve the opportunity to clarify them, as I am confident they will do."

'Violation' of arms embargo

Leon was appointed in 2014 to lead UN efforts to form a unity government between Libya's rival factions, based in Tripoli and Tobruk, respectively.

The envoy in July accepted a high-paying position as the first director of the government-funded Emirates Diplomatic Academy in Abu Dhabi, just as he was negotiating the final draft of the power-sharing deal.

Leon's controversial appointment was announced last week in a report by the Guardian, but the UAE's alleged role in supplying weapons came to light only on Thursday.

Inside Story: Have UN-led talks in Libya been compromised?

The emails reported on referred to an Emirates-based company, Morrison Commodities, that violated the arms embargo in Libya, possibly in cooperation with a Saudi firm called Saudi International Military Services.

One email quoted by the Times appears to be from a senior UAE diplomat who admitted his own country "violated the UN Security Council Resolution on Libya and continues to do so".

The UAE's support for the Tobruk-based government in Libya has already been well-documented, with allegations surfacing a year ago that the Gulf country carried out air strikes against Tripoli with the help of Egypt.

Peace deal under threat?

The UAE's minister of state for foreign affairs, Anwar Gargash, said in a statement: "UAE has consistently supported the process for peace and moderation in the effort towards a successful transition that benefits the Libyan people and the region."

Gargash did not respond directly to the allegations, but said: "UAE acknowledges the leadership of the UN secretary-general and commends the work and patience of his outgoing UN envoy Bernardino Leon, and his diligent pursuit of a political settlement in Libya throughout the difficult process and believes that his fortitude and professionalism should be recognised."

Under the power-sharing deal negotiated by Leon, Libya will be governed by a nine-member presidential council made up of a prime minister, five deputy prime ministers, and three senior ministers.

But the agreement has yet to win the full endorsement of all sides.

The president of the Tripoli-based administration, Nouri Abusahmain, last week accused Leon of bias in his mediation and called into question the peace deal.

A new envoy, Martin Kobler of Germany, is due to replace Leon in the coming days.